If they are to be given a colored finish, cement- and lime-bonded building materials, such as plasters, lime-sand bricks, fiber-reinforced cement parts or cast stones, more particularly roof tiles and paving setts and also flagstones, are generally colored with inorganic pigments. Thus, it is standard practice in the building industry to use iron oxides or iron oxide hydroxides as red, black, brown or yellow pigments, manganese oxides as brown-black pigments, chromium oxides as green pigments and titanium dioxides as white pigments. Further examples include carbon blacks as black pigments, nickel or chrome rutiles as yellow pigments and cobalt-containing spinels as blue and green pigments, copper-containing spinels as black pigments and mixed crystals of barium sulfate and barium manganate as blue pigments.
The pigments are normally used in powder form for coloring concrete products. In ground form, they have the advantage of ready dispersibility. The pigment powders are homogeneously distributed in concrete mixtures in a short time (up to a few minutes). The disadvantage of these fine powders is that they show unsatisfactory flow behavior and often agglomerate and form lumps during storage. This makes accurate dosing very difficult. Another disadvantage of certain powders is that they tend to emit dust.
It is known that these disadvantages can be avoided in the pigmenting of concrete products by using aqueous pastes or slurries instead of dry pigment powders. The use of these pastes or slurries, which contain from 30 to 70% by weight pigment, has never been entirely successful because the additional water content causes considerably higher transport costs, depending on the distance from the point of manufacture to the point of use. In addition, the large quantity of water supplied with the pastes or slurries cannot be processed in every concrete preparation. The content of organic chemicals can also be problematical.
Accordingly, the building materials industry has largely continued using dry pigment powders. Pigments in the form of microgranules have not hitherto been used because it was thought that granules would be less readily dispersible in concrete preparations. Poorly dispersible pigment agglomerates require much longer mixing times. With the short mixing times typically used in the building materials industry, speckles, streaks or color spots occur on the surface of the concrete due to poor pigment distribution. The coloring strength of the pigment cannot be developed, so that relatively large quantities of pigment have to be used for the same color intensity of the concrete product.
DE-C 3 619 363 describes pigment granules consisting essentially of pigment and one or more binder(s) promoting the dispersion of the pigment in the concrete for the coloring of concrete products. Suitable binders, which act as dispersion aids in the concrete, are said to be alkyl benzenesulfonate, alkyl naphthalenesulfonate, lignin sulfonate, sulfated polyglycol ethers, melamine/formaldehyde condensates, naphthalene/formaldehyde condensates, gluconic acid, salts of low molecular weight, partly esterified styrene/maleic anhydride copolymers and copolymers of vinyl acetate and crotonic acid. The percentage content of binder in the pigment is said to be preferably 2 to 6% by weight.
The dispersion aids mentioned act as plasticizers in concrete mixtures. They influence the water-to-cement ratio and act on the consistency of the concrete.
In the inorganic pigment itself, the binders added-- as organic substances--represent foreign material.
According to DE-A 2 940 156, the inorganic starting pigment has a resin content of at least 20%. The distribution of corresponding granules in concrete is seriously complicated by the resin components of hydrophobicized agglomerates.
DE-C 3 918 694 describes a process for coloring building materials with inorganic pigments in the form of microgranules, in which compounds of B, Al, Si, Ti, Zn and Sn are added to the pigments. This addition naturally incurs costs.
Now, the problem addressed by the present invention was to provide a process for coloring building materials which would not have any of the described disadvantages of the prior art.